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The biological response of human microvascular endothelial cells (HMEC-1) seeded on Si-DLC films and on control surfaces was evaluated in terms of initial cell enhancement, growth, and cytotoxicity. The microstructure of the films was characterised by Raman spectroscopy and X-ray photoelectron spectroscopy. The effect of changes in microstructure, surface energy, surface electronic state, and electronic conduction, on the biological response of the films to endothelial cells was investigated. Endothelial cell adhesion and growth was found to be affected by changes in the microstructure of the films induced by silicon doping and thermal annealing. We observed a significant statistical difference in endothelial cell count between the as-deposited DLC and Si-DLC films using the one sample t-test at a p-value of 0.05. We also found a statistically significant difference between the adhesion of HMEC films on DLC and Si-DLC films at various annealing temperatures using the one-way ANOVA F statistic test at p < 0.05 and the post-hoc Tukey test. One sample t-test at p < 0.05 of MTT-assay results showed the endothelial cells to be viable when seeded on DLC/Si-DLC films. We suspect that the increased adhesion of endothelial cells induced by increasing the amount of silicon in the Si-DLC films is associated with the development of a suitable surface energy due to silicon addition, which neither favored cell denaturing nor preferential water spreading before cellular attachment on the film surface. The presence of an external positively charged dipole on the Si-DLC films confirmed by our Kelvin probe measurements is also expected to enhance the adhesion of endothelial cells that are well known to carry a negative charge. The Si-DLC films investigated hold potential promise as coatings for haemocompatible artificial implants.

Diamond-like carbon (DLC) films have been proposed as potential coatings for blood-contacting devices. In this study, tetrahedral amorphous carbon (ta-C) films deposited by filtered cathodic vacuum arc system (FCVA) were compared with commercially deposited polyurethane coatings (PU) and uncoated stainless steel samples. X-ray reflectivity (XRR) measurements were performed to check density and thickness of the ta-C coatings, and contact angles measurements were used to assess surface wettability. J774 macrophages were used to assess the cell responses to the materials. Cell number, metabolic activity, and hydrogen peroxide production were measured by using biochemical assays, and the cell attachment and morphology were determined by using scanning electron microscopy and confocal laser scanning microscopy. Wettability measurements showed that of the materials, the stainless steel was the most hydrophilic, and the ta-C coatings were the most hydrophobic. Although the initial attachment and morphology did not appear to be dependent on the wettability, the cell numbers did increase with increasing wettability. Macrophages on the stainless steel samples were the most active in producing hydrogen peroxide. These data show that ta-C samples performed as well as commercial PU-coated samples in blocking cell reactions to the substrate and may prove to be effective coatings for blood-contacting materials., (Copyright 2004 Wiley Periodicals, Inc.)

Thin film technology takes more and more importance in the development of biomedical devices dedicated to functional neurostimulation. Our research about the design of implant neurostimulating electrode is oriented toward thin film cuff electrodes based on a polyimide substrate covered by a chromium/gold/Pt film. The chromium/gold sputtered film serves as adhesion layer and current collector whereas platinum acts as an electrochemical actuator. The electrode surface has been designed to obey safe stimulation criteria (i.e. chemically inert noble metal, low electrode-electrolyte impedance, high electrochemical reversibility, high corrosion stability). The electrochemical behaviour of such platinum electrodes has been assessed and compared to a foil of platinum. Extensive in vitro characterisations of the both electrode types were carried out using AFM, SEM and electrochemical techniques. The role of enhanced surface roughness enabling high double layer capacitances to be achieved was clearly highlighted. The obtained results are discussed, with particular reference to thin film electrodes stability under in vitro electrical stimulation in NaCl 0.9% (physiological serum). Therefore, these thin film devices showed reversible PtOH formation and decomposition making them potentially attractive for the fabrication of implant stimulation cuff electrodes.